Process for the production of paper, board and cardboard having high dry strength

Abstract

Process for the production of paper, board and cardboard having high dry strength by separate addition of a water-soluble cationic polymer and of an aqueous dispersion of a water-insoluble polymer having a content of acid groups of not more than 10 mol % or of an aqueous dispersion of a nonionic polymer, which dispersion has been made anionic, to a paper stock, draining of the paper stock and drying of the paper products. Preferably, the polymers are added to a paper stock which has a temperature of at least 40° C.

We claim: 
     
       1. A process for producing paper, board, or cardboard having high dry strength, the process comprising:
 separately adding a water-soluble cationic polymer and an anionic polymer to a paper stock; 
 draining the paper stock, to give a paper product and 
 drying of the paper product, 
 wherein the anionic polymer is at least one selected from the group consisting of an aqueous dispersion of a water-insoluble polymer having a content of acid groups of not more than 10 mol %, and an aqueous dispersion of a nonionic polymer, which aqueous dispersion has been made anionic. 
 
     
     
       2. The process according to  claim 1 , wherein the water-insoluble polymer has a content of acid groups of from 0.1 to 9 mol %. 
     
     
       3. The process according to  claim 2 , wherein the water-insoluble polymer has a content of acid groups of from 0.5 to 6 mol %. 
     
     
       4. The process according to  claim 3 , wherein the water-soluble polymer has a content of acid groups of from 2 to 6 mol %. 
     
     
       5. The process according to  claim 2 , wherein the water-soluble polymer has a content of acid groups of from 2 to 6 mol %. 
     
     
       6. The process according to  claim 2 , wherein the acid groups are selected from the group consisting of carboxyl groups, sulfophonic acid groups, and phosphonic acid groups. 
     
     
       7. The process according to  claim 1 , wherein the water-insoluble polymer has a content of acid groups of from 0.5 to 6 mol %. 
     
     
       8. The process according to  claim 7 , wherein the water-soluble polymer has a content of acid groups of from 2 to 6 mol %. 
     
     
       9. The process according to  claim 7 , wherein the acid groups are selected from the group consisting of carboxyl groups, sulfophonic acid groups, and phosphonic acid groups. 
     
     
       10. The process according to  claim 1 , wherein the water-soluble polymer has a content of acid groups of from 2 to 6 mol %. 
     
     
       11. The process according to  claim 1 , wherein the acid groups are selected from the group consisting of carboxyl groups, sulphonic acid groups, and phosphonic acid groups. 
     
     
       12. The process according to  claim 1 , wherein the anionic polymer comprises, in polymerized form:
 (a) at least one monomer selected from the group consisting of a C 1 - to C 20 -alkyl acrylate, a C 1 - to C 20 -alkyl methacrylate, a vinyl ester of a saturated carboxylic acid comprising up to 20 carbon atoms, a vinylaromatic having up to 20 carbon atoms, an ethylenically unsaturated nitrile, a vinyl ether of a saturated, monohydric alcohol comprising 1 to 10 carbon atoms, a vinyl halide and an aliphatic hydrocarbon having 2 to 8 carbon atoms and one or two double bonds; 
 (b) at least one anionic monomer selected from the group consisting of an ethylenically unsaturated C3- to C8-carboxylic acid, vinylsulfonic acid, acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylphosphonic acid, a salt of an ethylenically unsaturated C3- to C8 carboxylic acid, a salt of vinylsulfonic acid, a salt of acrylamido-2-methylpropanesulfonic acid, a salt of styrenesulfonoic acid, and a salt of vinylphosphoinic acid; optionally, 
 (c) at least one monomer selected from the group consisting of a C 1 - to C 10 -hydroxyalkyl acrylate, a C 1 - to C 10 -hydroxyalkyl methacrylate, acrylamide, methacrylamide, a N—C 1 - to C 20 -alkylacrylamide, and an N—C 1 - to C 20 -alkylmethacrylamide; and, optionally, 
 (d) at least one monomer having at least two ethylenically unsaturated double bonds in the molecule. 
 
     
     
       13. The process according to  claim 1 , wherein the anionic polymer comprises, in polymerized form:
 (a) at least 60 mol % of at least one monomer selected from the group consisting of a C 1 - to C 20 -alkyl acrylate, a C 1 - to C 20 -alkyl methacrylate, vinyl acetate, vinyl propionate, styrene, .alpha.-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, acrylonitrile, methacrylonitrile, butadiene, and isoprene; and 
 (b) from 0.5 to 9 mol % of at least one anionic monomer which is an ethylenically unsaturated C 3 - to C 5 -carboxylic acid. 
 
     
     
       14. The process according to  claim 1 , wherein the anionic polymer comprises, in polymerized form, at least 80 mol % of at least one monomer selected from the group consisting of
 (a) at least one monomer selected from the group consisting of a C 1 - to C 20 -alkyl acrylate, a C 1 - to C 20 -alkyl methacrylate, a vinyl ester of a saturated carboxylic acid comprising up to 20 carbon atoms, a vinylaromatic having up to 20 carbon atoms, an ethylenically unsaturated nitrile, a vinyl ether of a saturated, monohydric alcohol comprising 1 to 10 carbon atoms, a vinyl halide, and an aliphatic hydrocarbon having 2 to 8 carbon atoms and one or two double bonds. 
 
     
     
       15. The process according to  claim 14 , wherein the anionic polymer comprises, in polymerized form as (a), a mixture of
 (i) a C 1 - to C 20 -alkyl acrylate and/or a C 1 - to C 20 -alkyl methacrylate, and 
 (ii) styrene, α-methylstyrene, p-methylstyrene, α-butylstyrene, 4-n-butylstyrene, butadiene, and/or isoprene, 
 in a weight ratio of from 10:90 to 90:10. 
 
     
     
       16. The process according to  claim 1 , wherein the anionic polymer has a glass transition temperature T g  of from −30 to 100° C., measured according to DIN EN ISO 11357. 
     
     
       17. The process according to  claim 1 , wherein the anionic polymer has a glass transition temperature of from −5 to 70° C. 
     
     
       18. The process according to  claim 1 , wherein a temperature of the paper stock is at least 40° C. 
     
     
       19. The process according to  claim 1 , wherein a temperature of the paper stock is at least 50° C. 
     
     
       20. The process according to  claim 1 , wherein a polymer having polymerized vinylamine units is the water-soluble cationic polymer.